A phase frequency detection device disclosed in Patent Literature 1 mentioned later is constituted by A/D conversion circuitry, a digital BPF, delay compensation circuitry, Hilbert transformation circuitry, phase angle computation circuitry, a memory, and frequency computation circuitry.
The A/D conversion circuitry converts an input analog signal into a digital signal and outputs the digital signal to the digital BPF.
The digital BPF outputs only a digital signal in a desired frequency band among digital signals output by the A/D conversion circuitry to the delay compensation circuitry and the Hilbert transformation circuitry.
After receiving the digital signal of the desired frequency band from the digital BPF, the delay compensation circuitry performs a time-shift of the digital signal by a time corresponding to a delay time caused by a Hilbert transformation in the Hilbert transformation circuitry.
After receiving the digital signal of the desired frequency band from the digital BPF, the Hilbert transformation circuitry performs a Hilbert transformation on the digital signal, and thereby outputs a signal differing from the digital signal in a phase by 90 degrees.
Note that the higher the accuracy required for the amplitude and phase of an output signal from the Hilbert transformation circuitry, the longer the delay time resulting from a Hilbert transformation. Therefore, the number of stages of delay circuitry included in the delay compensation circuitry increases, resulting in several tens to hundreds of stages.
The phase angle computation circuitry computes a phase of the input analog signal by performing an arctangent computation based on the output signal of the delay compensation circuitry and the output signal of the Hilbert transformation circuitry, and outputs the resulting phase to the memory and the frequency computation circuitry.
The frequency computation circuitry computes a frequency of the input analog signal by using the phase output by the phase angle computation circuitry and a phase obtained at one sampling time before, which has been stored in the memory.